/*
 * Copyright (c) 2011-2014 Pivotal Software, Inc.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
package org.camunda.bpm.extension.reactor.projectreactor.support;

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;
import java.util.UUID;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Helper for creating random and Type 1 (time-based) UUIDs.
 *
 * @author Jon Brisbin
 */
public abstract class UUIDUtils {

  private static boolean IS_THREADLOCALRANDOM_AVAILABLE = false;
  private static Random random;
  private static final long leastSigBits;
  private static final ReentrantLock lock = new ReentrantLock();
  private static long lastTime;

  static {
    try {
      IS_THREADLOCALRANDOM_AVAILABLE = null != UUIDUtils.class.getClassLoader().loadClass(
        "java.util.concurrent.ThreadLocalRandom"
      );
    } catch (Throwable t) {
    }

    byte[] seed = new SecureRandom().generateSeed(8);
    leastSigBits = new BigInteger(seed).longValue();
    if (!IS_THREADLOCALRANDOM_AVAILABLE) {
      random = new Random(leastSigBits);
    }
  }

  private UUIDUtils() {
  }

  /**
   * Create a new random UUID.
   *
   * @return the new UUID
   */
  public static UUID random() {
    byte[] randomBytes = new byte[16];
    if (IS_THREADLOCALRANDOM_AVAILABLE) {
      java.util.concurrent.ThreadLocalRandom.current().nextBytes(randomBytes);
    } else {
      random.nextBytes(randomBytes);
    }

    long mostSigBits = 0;
    for (int i = 0; i < 8; i++) {
      mostSigBits = (mostSigBits << 8) | (randomBytes[i] & 0xff);
    }
    long leastSigBits = 0;
    for (int i = 8; i < 16; i++) {
      leastSigBits = (leastSigBits << 8) | (randomBytes[i] & 0xff);
    }

    return new UUID(mostSigBits, leastSigBits);
  }

  /**
   * Create a new time-based UUID.
   *
   * @return the new UUID
   */
  public static UUID create() {
    long timeMillis = (System.currentTimeMillis() * 10000) + 0x01B21DD213814000L;

    lock.lock();
    try {
      if (timeMillis > lastTime) {
        lastTime = timeMillis;
      } else {
        timeMillis = ++lastTime;
      }
    } finally {
      lock.unlock();
    }

    // time low
    long mostSigBits = timeMillis << 32;

    // time mid
    mostSigBits |= (timeMillis & 0xFFFF00000000L) >> 16;

    // time hi and version
    mostSigBits |= 0x1000 | ((timeMillis >> 48) & 0x0FFF); // version 1

    return new UUID(mostSigBits, leastSigBits);
  }

}
